1. Field of the Invention
This invention concerns a process for the deactivation of certain biocides which are used for the treatment of water.
2. Background Information
In our patent GB 2145708 we have described the use of certain hydroxy alkyl phosphines and phosphonium salts as biocidal agents against bacteria, algae, fungi and other lower organisms. These compounds may be used in cooling and other systems which contain water for prolonged periods, and may prevent the build-up of living organisms which would otherwise reduce the efficiency of such systems. As outlined in EP 0293152, these compounds can also be applied for the purposes outlined above to ecologically sensitive systems containing higher life-forms such as fish, without causing them any harm. An advantage of the compounds is that they achieve a rapid kill of the target organism whilst having a relatively low toxicity to higher organisms such as fish.
However, in systems in which treated water is discharged as effluent it would be advantageous to deactivate these biocides prior to discharge. It is known that certain hydroxy alkyl phosphines and phosphonium salts react with dissolved oxygen and are thereby deactivated in acidic water. This property is not directly applicable to water systems, such as cooling systems, which are often operated at a higher pH e.g. 7 to 10. In this pH range the oxidative decomposition of the biocides essentially does not proceed. It is possible to acidify the effluent before discharge, and allow the oxidation to occur but subsequent adjustment to a neutral pH would be required before discharge. This process would be cumbersome, require continuous tight control and would be costly in terms of acid and alkali consumption. In addition the dissolved solids level in the discharged water would be increased.